So I'm not really quite sure what Landis' plans were to make another one. The American Werewolf in Paris was a completely separate story.
In truth I don't think when Landis wrote An American Werewolf he ever wrote it in terms as having an ongoing story, he wrote it as a complete piece.
Clearly any film company that makes a film is always going to talk about sequels particularly if they see something as being successful, which Werewolf was.